Add invokable public API for emitting contextualActionsAboutToShow

Summary:
This signal is emitted just before showing the context menu to allow
lazy-loading expensive actions like hasAlternatives.

This emitted by our code whenever we show a context menu from an event
filter, however we want to use this code from a tooltip in D17410

Test Plan:
Hovered over some applets, they correctly enabled/disabled the
alternatives button

Reviewers: #plasma

Subscribers: kde-frameworks-devel

Tags: #frameworks

Differential Revision: https://phabricator.kde.org/D20417

src/scriptengines/qml/plasmoid/appletinterface.cpp

@@ -784,6 +784,11 @@ bool AppletInterface::event(QEvent *event)
     return AppletQuickItem::event(event);
 }
 
+void AppletInterface::prepareContextualActions()
+{
+    emit applet()->contextualActionsAboutToShow();
+}
+
 bool AppletInterface::eventFilter(QObject *watched, QEvent *event)
 {
     if (event->type() == QEvent::MouseButtonPress) {
@@ -825,7 +830,7 @@ bool AppletInterface::eventFilter(QObject *watched, QEvent *event)
             if (desktopMenu->winId()) {
                 desktopMenu->windowHandle()->setTransientParent(window());
             }
-            emit applet()->contextualActionsAboutToShow();
+            prepareContextualActions();
             ci->addAppletActions(desktopMenu, applet(), event);
 
             if (!desktopMenu->isEmpty()) {

src/scriptengines/qml/plasmoid/appletinterface.h

@@ -277,6 +277,14 @@ public:
 
     Q_INVOKABLE QAction *action(QString name) const;
 
+    /**
+     * Should be called before retrieving any action
+     * to ensure contents are up to date
+     * @see contextualActionsAboutToShow
+     * @since 5.58
+     */
+    Q_INVOKABLE void prepareContextualActions();
+
     /**
      * FIXME: remove?
      * Retrieve the path of a file from the Plasmoid package